On Jun 8, 5:50 am, Ondrej Certik <[email protected]> wrote:
>
> I agree that some deep backtrace is confusing, especially if it's
> something that the users do frequently.
>
> Could you please paste here the exact output, so that we can discuss
> some particular example?
>
###
>>> from sympy import *
>>> x=var('x')
>>> roots(1/x,x).keys()
Traceback (most recent call last):
File "<interactive input>", line 1, in <module>
File "C:\Documents and Settings\chris\sympy\sympy\polys
\rootfinding.py", line 190, in roots
f = Poly(f, *symbols)
File "C:\Documents and Settings\chris\sympy\sympy\polys
\polynomial.py", line 402, in __new__
terms = Poly._decompose(poly, *symbols)
File "C:\Documents and Settings\chris\sympy\sympy\polys
\polynomial.py", line 545, in _decompose
raise PolynomialError("Can't decompose %s" % factor)
PolynomialError: Can't decompose 1/x
###
OK, that's not to obtuse. You know what the routine was trying to do
and you learn that poly can only change things thare are x**m-like in
appearance.
But, knowing that roots like to have a poly, if you try to send it a
poly then...
###
>>> roots((1/x).as_poly(x))
Traceback (most recent call last):
File "<interactive input>", line 1, in <module>
File "C:\Documents and Settings\chris\sympy\sympy\polys
\rootfinding.py", line 190, in roots
f = Poly(f, *symbols)
File "C:\Documents and Settings\chris\sympy\sympy\polys
\polynomial.py", line 300, in __new__
raise SymbolsError("No symbols were given")
SymbolsError: No symbols were given
###
The poly that you sent (which here is obviously not x**m-like, but
could have been an expression generated along the way in some
computation) *was not a poly* (it was None because the poly step
failed) and it complains that no symbols were given when clearly a
symbol was given.
So I don't know...perhaps that lesson would have been not to try to do
too much of the work (i.e. making it into a poly first). Or perhaps
rootfinding should have complained that no function was received
rather than passing off the None and "no symbol" to poynomial and
getting a complaint from there that "there was no symbol".
/c
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